1. Field of the Invention
The present invention relates to a metal-suitable RFID tag and an RFID tag unit, and in particular to an RFID tag unit separable from a metal-suitable RFID tag and allowing a printing and issuing, and to a metal-suitable RFID tag comprising the aforementioned RFID tag unit.
2. Description of the Related Art
Currently there is an increasing interest in Radio Frequency Identification (RFID) tags. The RFID tag is a type of a wireless integrated circuit (IC) tag, and is constituted of components including a large scale integrated circuit (LSI) chip, an antenna, and an external resin for molding the aforementioned components. The external size of an RFID tag varies widely, e.g., from 0.3 mm (the size of a sesame seed) to 20 to 30 mm (the size of a coin) in diameter, the size of an IC card. Also, there is a battery built-in type and there is a non battery built-in type. The former is called an active type tag and the latter is called a passive type tag.
An LSI chip built in the RFID tag comprises an antenna, a transmission/reception unit, a control unit and a memory. The memory stores a specific identification code (i.e., a unique ID) which is read by an RFID tag-use reader/writer (simply noted as “reader/writer” hereinafter). The readout of the unique ID of the RFID tag by the reader/writer is carried out by a radio communication via an RFID tag-use antenna (simply noted as “antenna” hereinafter). The radio communication employs a radio wave method or an electromagnetic induction method.
The characteristics of an RFID tag are usually greatly altered when it is attached to a metal. As an example, in the case of an RFID tag of the electromagnetic induction method, an eddy current flows when a magnetic flux enters a metal so that the eddy current acts in negating the magnetic flux. As a result, the communication range is greatly decreased, and, in the worst case, communicating becomes impossible. In such a case, an impact of a metal is eliminated if the attaching position of the RFID tag is separated from the metal by a certain distance.
Meanwhile, in the case of an RFID tag of the radio wave method, a multi-pass phenomenon is generated as a result of a radio wave reflecting on a metal surface. The multi-pass phenomenon causes readout of information stored in the RFID tag to be unstable and a degradation of a power conversion efficiency of the antenna of the RFID tag, thereby degrading a communication ranges as in the case of the electromagnetic induction method.
Also in this case, an influence of a metal can be mitigated if the attaching position of the RFID tag is separated from the metal by a certain distance.
In the cases of a commercial products or other products, many are made from metallic materials. Therefore, there is metal-suitable RFID tag that can be put on the metal, and it has already been commercialized.
The metal-suitable RFID tag is configured to attach to a metal by keeping the antenna (i.e., the RFID tag antenna) clear of the metal in a suitable distance or sandwiching an RF absorption material between the RFID tag and the metal.
FIG. 1 is a vertical cross-section diagram showing a composition of a conventional metal-suitable RFID tag 100.
The metal-suitable REID tag 100 shown in FIG. 1 is configured so as to layer a metal reflection plate 101, a spacer 102, a substrate material part 103 and a PET(polyethylene terephthalate) material 104 in the aforementioned order.
The substrate material part 103 is incorporated with an RFID tag which is equipped with an LSI chip 111 at the approximate center thereof and an antenna (i.e., RFID tag antennas) 112 on both side surfaces. The RFID tag is constituted of the LSI chip 111 and antenna 112. The LSI chip 111 is integrated with a control part, a transmission/reception part, a memory and such. A dipole antenna is widely used as the antenna 112.
The metal reflection plate 101, being a thin plate attached to a metal via an adhesive (not shown in a drawing herein), reflects an RF reflected on the aforementioned metal. The spacer part 102, comprising a dielectric body and a Styrofoam, plastic or such, is for keeping enough space between the metal, to which the metal-suitable RFID tag 100 is attached, and the antenna 112 incorporated in the substrate material part 103. For example, a material having the function as an RF absorption member is used as a material for the space part 102.
The conventional metal-suitable RFID tag 100 as configured above needs to increase the thickness of the spacer part 102, therefore the thickness of the metal-suitable RFID tag 100 increase in size as a result, its handling is difficult and its usage is limited. Further it is bulky and poorly flexible, hence precluding a printing/issuing by using a label printer (i.e., an RFID tag-use label printer).
Here, an “issuing” means the process of writing data to an RFID tag (including a metal-suitable RFID tag) and of printing. Also an RFID tag-use label printer has a built-in reader/writer function and is capable of writing data to an RFID tag and printing it.
The conventional metal-suitable RFID tag requires a writing of specific data individually by using a reader/writer due to the above described reasons. A printing on the metal-suitable RFID tag is limited to a printing in a lump at the production thereof or attaching a printed label thereto.
Incidentally, a known invention similar to the present invention is a composite body installable to a metallic body by using a pressure sensitive resin material after forming a composite body comprising a layer including an RFID and a layer which is formed on the aforementioned layer and which has a printable surface and printing a surface of the composite body (refer to a reference patent document 1).
Another known invention is a data carrier which employs either an electromagnetic induction method or a microwave method and which is directly mountable onto a metal surface; and a data carrier-use adaptor which integrates an upper layer constituted of a ferrite layer and a lower layer comprised of a good conductive metal layer and which is mountable onto a metal by attaching onto the back of the data carrier (refer to a reference patent document 2).
Yet another known invention is a method capable of adjusting a tuning frequency of a data carrier by attaching a metallic seal of a prescribed size to a prescribed position of a coil operating synchronously with a predetermined frequency (refer to a reference patent document 3).
Yet another known invention is a noncontact type data carrier comprising an IC chip and an antenna, in which a resonance frequency of a resonance circuit is adjustable. The noncontact type data carrier is configured to suppress a variation of a resonance frequency caused by a variation of capacitance of an IC chip constituting a resonance circuit of the data carrier by adjusting inductance of the antenna that is a part of the components constituting the resonance circuit. The specific composition is to adjust the inductance of the antenna by placing components, such as a closed loop antenna, a conductor (such as a metal) and a separate resonance circuit near the antenna (refer to a reference patent document 4).
Patent document 1: Japanese Unexamined Patent Application Publication Translations of PCT Application No. 2004-510190
Patent document 2: Laid-Open Japanese Patent Application Publication No. 2001-68916
Patent document 3: Laid-Open Japanese Patent Application Publication No. 2003-271913
Patent document 4: Laid-Open Japanese Patent Application Publication No. 2001-160124